by EG McPherson, JR Simpson, Q Xiao, C Wu
Landscape and Urban Planning 99:40-502011
In 2006, the mayor of Los Angeles kicked off an initiative to plant one million trees. The authors of this study attempted to answer a number of questions raised by the project: How many trees are there in LA? Is there room for a million more? What benefits could be expected from the project? Quickbird remote sensing data, aerial imagery and GIS data were used (1) to classify land cover (from which the number of trees was estimated), (2) to determine the number of available planting spaces (i.e., areas classified as bare soil or grass and not immediately adjacent to impervious surfaces), and (3) to estimate the ecosystem services of an additional one million trees in terms of energy conserved, CO2 reductions, air quality improvement, stormwater runoff reduction, and aesthetics and other benefits. High and low mortality scenarios were presented, and benefits were projected for 35 years. Tree canopy cover at the time of the study was 21%, representing 10.8 million trees, and differed strongly by land use and council district. Across the city, 2.5 million available planting spaces were found. The proposed one million trees were projected to provide between $1.3 and 1.9 billion in benefits over a 35-year period (depending on mortality rate).